Mounting evidence demonstrates that weight influences intimate (i.e., dating and sexual) relationship formation and sexual negotiations among adolescent girls. Obese girls consistently report having fewer dating and sexual experiences, but more sexual risk behaviors (i.e., condom nonuse) once they are sexually active. The conceptual framework that has guided this research presumes that differences in the social skills for relating to peers and intimate partners along with differences in the relationship experiences of obese and non-obese girls account for these differences. However, no studies have actually examined whether the interpersonal skills and intimate relationships of obese and non-obese girls differ. We propose to address this research gap by conducting a secondary data analysis using data from two large, longitudinal cohorts of U.S. adolescent girls. We use the National Longitudinal Survey of Adolescent Health (Add Health), a nationally representative cohort study conducted between 1994 and 2008; and the Pittsburgh Girls Study (PGS), an on-going population-based cohort study started in 2000, and conducted in a setting with high rates of adolescent sexual risk-taking and high rates of adolescent obesity. Our specific aims are to (1) determine whether obese adolescent girls experience a delay in the development of peer and intimate relationship skills compared to non-obese adolescent girls; (2) compare the characteristics of intimate relationships among obese and non-obese adolescent girls; (3) use longitudinal growth curve modeling to determine whether trajectories of romantic and sexual relationship characteristics differ between obese and non-obese adolescent girls over time; (4) determine how peer and intimate relationship skills affect trajectories of intimate relationships among obese and non-obese adolescent girls over time; and, (5) compare the development of interpersonal skills and intimate relationship characteristics between obese and non-obese African American and White adolescent girls. INNOVATION: Our proposal is innovative as it is the first study to explore relationship context as a mechanism linking obesity to adolescent girls' sexual risk-taking behaviors. Our use of two complementary datasets - one nationally representative cohort and one population-based cohort from a high risk setting - will allow us to identify nuances that are important for crafting a more complete understanding of the role that social skills and relationship experiences play in explaining variations in the sexual behaviors of obese and non-obese adolescents. We take a developmental approach by examining how relationship experiences evolve over time. Finally, by exploring how relationship experiences differ among African American and White adolescent girls, our approach acknowledges that cultural differences in beauty norms exist and are important. PUBLIC HEALTH SIGNIFICANCE: The overarching goal of this research is to expand the conceptual framework linking weight to adolescent sexual risk-taking thereby providing critical information useful for tailoring adolescent sexual risk-reduction interventions and sexual negotiation skills building programs.